Inadmissible consumption of limited resources, contamination of water, air pollution, overpopulation.
A meteor strike like the ones that wiped out the dinosaurs would truly challenge civilization’s ability to cope. Tens of millions would die in the strike and subsequent effects like earthquakes, dust and tsunamis. Then an ice age would set it. We are overdue and scientists are warning us we are badly unprepared for such an event. @icedrum